This is a prospective study of the effects of lead exposure on the physical and mental health of children. It is composed of both human and animal studies. The study of children is to be conducted in the natural environmental setting where elevated lead exposure is common. We hope to establish whether and under what environmental circumstances lead causes adverse health effects. Prospective mothers will be recruited into the study during the first or second trimester of pregnancy. Their offspring will be followed for five years. Since many factors are known to influence the behavioral and intellectual development of a child, a multivariate design will be used rather than design which employs a control versus experimental group comparison. Data to be collected on each child include; prenatal and delivery records; physical growth, behavioral and intellectual profiles beginning at 3 days of age and repeated at 9 month intervals; blood lead, FEP, and iron status at 3 month intervals; evaluation of the home environment with respect to quality of child care and sources of lead exposure. The animal studies will use rats exposed perinatally to low levels of lead. Tissue and blood will be monitored for lead and trace metal content. Other measures will include neurotransmitter metabolism, electrophysiological assessment and behavioral evaluation. The animal studies will explore critical periods, persistence and reversibility of toxicity and the utility of hematopoietic indices for identifying individuals at risk for subsequent behavioral impairment. Both human and animal studies will examine the role of age, duration and levels of lead exposure as determinants of effect as well as exploring leads interaction with numerous environmental variables as a determinant of toxicity. The ultimate purpose of all research on neurobehavioral effects of lead is to establish the minimal level of exposure at which effects may occur, as reflected in biological indices e.g. blood lead. A prospective study of the type proposed is necessary to answer crucial questions pertaining to the maximal safe level of exposure at any time in the child's life. Only with such a study can regulatory agencies institute proper control of exposure.